The actual dimensions of the nucleus present in the atom are called nuclear size. Various experiments have been done to determine the size of nucleus (eg- Rutherford’s experiment). The nuclear size can be determined as-
r = RoA1/3
Where r is the radius of nucleus and A is the mass no. of atom and R0 is constant whose value is 1.5*10-13cm or 1.5*10-15m. The nuclear radius is of order of 10-14, therefore very small. It is measured in Fermi units.